1. Field of the Invention
This invention relates to an information recording/reproducing apparatus such as an optical disc drive for recording information on and retrieving stored information from an information recording medium, or an optical disc, that is provided with sectors having a header section and a data section and arranged in a specific recording format such as CAV, CLV or MCAV and it also relates to an information recording medium to be used for such an apparatus.
2. Description of the Related Art
There are already known and put to practical use a variety of information recording/reproducing apparatuses for recording information on and retrieving stored information from an optical disc (information recording medium) having recording tracks by means of a laser beam emitted from a semiconductor laser disposed in an optical head.
Formats that are currently available for recording information on an information recording medium by means of an optical disc drive include CAV (constant angular velocity), CLV (constant liner velocity) and MACV (modified constant angular velocity). Of these, CLV and MCAV have much in common in that data are stored on a recording medium at a substantially uniform data density. With the CLV format, the optical disc is rotated at a rate of revolution that varies as a function of the distance from the center of the disc of the location where data is currently being recorded, whereas, with the MCAV format, the data clock frequency used for recording data is made to vary. It may be safe to say that CLV is adapted to recording music or moving pictures because a constant data clock frequency is involved, whereas any specific piece of information stored on an optical data can be accessed very quickly with MCAV because the disc is rotated at a constant rate and no change is involved in the rate of revolution of the disc.
However, these techniques are also accompanied by certain drawbacks. No large capacity for storing information can be realized with CAV, while CLV has a drawback of baffling any attempt for quick and frequent random access because the rate of revolution changes constantly. With MCAV, on other hand, the maximum value of the data clock frequency F to be used for recording and reproducing information is limited by the information recording/reproducing performance of the signal processing circuit of the apparatus so that, while the operation of recording or reproducing data may be quickly conducted in a peripheral area of the disc, it may not so in an inner area.
As summarized above, any of the known information recording formats of CAV, CLV and MCAV cannot satisfy the users of information recording/reproducing apparatuses of the type under consideration particularly in terms of capacity and performance because CAV cannot provide a large capacity and CLV is not capable of adapting itself to quick and frequent random access, while MCAV is not adapted to recording music or moving pictures because the operation of recording or reproducing data cannot be conducted in an inner area of the optical disc as the maximum value of the data clock frequency to be used for recording and reproducing information is limited by the information recording/reproducing performance of the signal processing circuit of the apparatus, although it may be conducted quickly in a peripheral area of the disc.